The present invention relates to a process apparatus for performing a process, such as etching, on an object such as a semiconductor wafer.
A magnetron-type plasma process apparatus that is generally known comprises a gas-tight process vessel, an upper electrode provided in the vessel, a lower electrode provided in the vessel and opposing the upper electrode, and a magnet surrounding a plasma region provided between the upper and lower electrodes.
To perform a plasma process on an object by the use of such a magnetron-type plasma process apparatus, the object is mounted on the lower electrode. Then, the process gas is introduced into the process vessel. The process vessel is evacuated, whereby a low-pressure atmosphere is maintained in the vessel. Thereafter, high-frequency power is supplied to the lower electrode, thereby generating plasma in the process vessel.
Generally, a plasma process apparatus of this type has a baffle plate, which partitions the process vessel into a process chamber and an exhaust passage. An object to be processed is placed in the process chamber. The exhaust passage communicates with an evacuation mechanism. The baffle plate is provided between the side of the lower electrode and the inner surface of the process vessel and surrounds the lower electrode. The baffle plate has a plurality of slits that extend in the radial direction, connecting the process chamber and the exhaust passage. (The chamber and the passage communicate with each other through these slits.) Thus, the baffle plate partitions the plasma region while the process is undergoing. This increases the density of plasma in the process chamber. Further, the conductance between the process chamber and the exhaust passage is maintained in a prescribed condition since the gas is guided from the chamber into the passage through the slits. Thus, the gas can be exhausted from the process chamber in a stable condition.
The baffle plate has the function of holding the reaction product made by the process, thus reducing the amount in which the reaction product flows into the exhaust passage. The reaction product deposits on that surface of the baffle plate which is exposed to the process chamber (i.e., the surface of the plate facing the chamber). The amount of deposition is proportional to the time of process. If the product deposits on the rims of the slits through which the gas flows from the process chamber, the slits will become narrower. Consequently, the pressure in the process chamber will rise. This impairs the uniformity of etching in the plane of the object (i.e., in-plane uniformity) or decrease the etching rate. To prevent such undesirable events, the maintenance of the baffle plate is effected at regular intervals, by either washing the plate or by replacing it with a new one. If the process generates deposit in large quantities, however, the maintenance must be carried out more frequently. In this case, the throughput of the process will decrease.
The object of the invention is to provide a novel, improved process apparatus in which the slits of the baffle plate are hardly narrowed with deposit on the chamber side, an atmosphere of a prescribed pressure can therefore be maintained in the process chamber for a long time (that is, the process time can be lengthened without changing the process conditions), and the maintenance cycle of the baffle plate can be thereby extended to enhance the throughput of the process.
To attain the object, a process apparatus according to the present invention includes an airtight process vessel, an exhaust system for exhausting gas from the process vessel, and a baffle plate for partitioning the process vessel into a process chamber for processing an object and an exhaust passage communicating with the exhaust system. The baffle plate has a plurality of slits through which the process chamber and the exhaust passage communicate with each other, and each of the slits has a tapered surface on an inner surface toward the process chamber, the tapered surface being formed to not less than xc2xc of a depth of the slit.
In particular, when the tapered surface is not less than xc2xd of the depth of the slit, it is preferable that angle xcex8 between the tapered surface and a perpendicular crossing an open end of the slit at right angles fall within a range from 5xc2x0 to 30xc2x0 (5xc2x0xe2x89xa6xcex8xe2x89xa630xc2x0).
When each slit has an enlarged opening facing the exhaust passage, extending from an opening rim of the slit, which faces the exhaust passage, toward the process chamber, and having an inside diameter which is larger than the minimum inside diameter of a process-chamber-side portion of the slit on which the tapered surface is formed, it is preferable that the tapered surface and the enlarged opening be each formed to xc2xc to xc2xd of the depth of the slit and angle xcex8 between the tapered surface and a perpendicular crossing an open end of the slit at right angles fall within a range from 30xc2x0 to 60xc2x0 (30xc2x0xe2x89xa6xcex8xe2x89xa660xc2x0). In this case, preferably, width W1 of an opening of the slit, which faces the process chamber, and width W2 of an opening of the slit, which faces the exhaust passage, are set so as to satisfy a condition of 1xe2x89xa6W2/W1xe2x89xa61.4.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.